Abstract: With the increasing pressure on water resources, grain security under the constraint of water resources is getting more and more attention. To have a better understanding of the contradiction between grain production and water resources, this article analyzes the spatio-temporal distribution of national grain output and total water resources and utilizes the barycenter model to explore the evolution trend and the spatio-temporal coupling degree of grain production barycenter and water resources barycenter from 1998 to 2018 at the national and regional levels. Results show that 1) China’s grain production barycenter has moved 238.78 km to the northeast from 1999 to 2018 and has displayed a trend of northward movement in both national and regional levels. The barycenter of water resources is always located in the southwest of grain production barycenter, without a large range of movement; 2) at the national level, the spatial distance between the barycenter of grain production and water resources has increased, meaning the spatial overlap degree of the two elements has decreased, but the increasing trend of the spatial distance has been subtle in recent years. The average value of the changing consistency index of the two barycenters is -0.03, indicating a relatively low matching level, however the mean value is 0.14 from 2014 to 2018, indicating the coupling degree is slightly enhanced; and 3) at the regional level, combined with the spatial distance and the changing consistency index of the two barycenters, the spatiotemporal coupling degree is the strongest in the northeast and the southwest regions, while it is weaker in the northwest region. This paper implies that optimizing planning of water resources utilization pattern and improving the utilization efficiency of water resources in grain production would help alleviate the tense relationship between grain production and water resources.